Semiconductor devices, from microprocessors to memory chips, are fabricated by performing a complex series of processes that include depositing various materials and selectively masking and etching one or more materials on portions of a semiconductor wafer or other bulk semiconductor substrate. Silicon is a conductive material that is commonly used as a semiconductor substrate in a semiconductor device, such as in an integrated circuit. Ideally, etching selectively removes or etches portions of the semiconductor substrate without damaging or removing other portions. In a wet etch process, a wet etch solution is typically applied to a surface of the semiconductor substrate. Reactants in the wet etch solution adsorb to the surface of the semiconductor substrate and react with the silicon surface. After the reaction has occurred, reaction byproducts desorb from the surface of the semiconductor substrate and are solubilized in the wet etch solution, removing portions of the semiconductor substrate. For instance, in a typical wet etch process of a semiconductor substrate formed from silicon, the reactants in the wet etch solution react with the silicon, forming an oxide layer on the surface of the silicon semiconductor substrate. The oxide layer is subsequently dissolved, effectively etching the surface of the silicon semiconductor substrate.
Etchants or wet etch solutions that etch silicon are typically aqueous solutions of alkaline bases, such as potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), or tetramethylammonium hydroxide (“TMAH”). U.S. Pat. No. 4,113,551 to Bassous et al. discloses an aqueous TMAH solution that selectively etches silicon relative to silicon dioxide (SiO2), poly SiO2, or phosphosilicate glass. U.S. Pat. No. 6,103,598 to Yamagata et al. discloses an aqueous TMAH solution that selectively etches porous monocrystalline silicon relative to SiO2. U.S. Pat. No. 5,565,060 to Austin et al. discloses an aqueous TMAH solution that includes a high flash point alcohol and selectively etches silicon relative to p-doped silicon. One example of a solution for etching silicon is BakerClean® JTB-111, which is available from J. T. Baker (Phillipsburg, N.J.). Solutions having ammonium fluoride, phosphoric acid, hydrogen peroxide, and deionized water have also been used to etch silicon. However, these etchants also aggressively etch other materials, such as metals, oxides, polyimides, or nitrides, which are commonly present on the substrate as portions of an integrated circuit being fabricated thereon. Therefore, if the integrated circuit includes metal features, these features are corroded or otherwise damaged by the etchant. Since these etchants are not particularly selective for silicon, they are not well suited for etching silicon when features formed from other materials are present on the substrate.
Aqueous TMAH solutions have also been used to clean metallic or organic contamination from semiconductor substrates, as disclosed in U.S. Pat. No. 6,465,403 to Skee. The cleaning solution includes TMAH, a water-soluble, metal ion-free silicate, a chelating agent and, optionally, a water-soluble organic solvent or a surfactant. Similarly, U.S. Pat. No. 5,466,389 to Ilardi et al. discloses an aqueous cleaning solution that includes TMAH, a nonionic surfactant, and a compound that reduces a pH of the cleaning solution to 8-10. U.S. Pat. No. 6,534,458 to Kakizawa et al. (“Kakizawa”) discloses an aqueous cleaning solution that includes TMAH, a nonionic surfactant, and an organic solvent. The cleaning solution is used to remove impurities that are absorbed onto copper wiring on a semiconductor substrate.
TMAH has also been used in photoresist compositions and photoresist developer compositions. For instance, U.S. Pat. No. 6,599,683 to Torek et al. discloses a photoresist developer that includes a polyhydric alcohol, such as propylene glycol, a base compound, such as TMAH, a surfactant, and water.